Rotation induced stabilization of air convection in a bottom heated diverging cylinder rotating about its own axis

Abstract

Rotation induced stabilization of air convection in a vertical, diverging cylinder heated from below and rotated steadily about its own axis is studied experimentally. The cylinder has a smaller circular cross section at its bottom end. In the experiments, the transient variations of the air temperature at selected locations are measured to explore the effects of rotation rate and diverging angle on the temporal stability of the flow. Data are collected for the diverging angle varied from 0-30 degrees, imposed temperature difference from 5-15 degrees C and rotation rate up to 346.1 rpm. The measured data show that the ranges of the rotation rate to stabilize the flow are wider for diverging cylinders than those fora right cylinder at xi = 0 degrees. Thus, it is possible to use a crucible with a diverging section to grow large and high quality bulk crystals. A power spectrum density analysis of the data for the unstable flow at high rotation rates indicates that the flow oscillation is mainly time periodic and dominated by a single fundamental frequency: Moreover, the oscillation frequency varies nonmonotonically with the rotation rate. Flow regime maps delineating stable and unstable states are also provided for practical applications. (C) 1998 Elsevier Science Ltd. All rights reserved.